1. Field of the Invention
The present invention relates to an automatic clearance compensation device for a support yoke of a rack-pinion type steering apparatus, and more particularly to an automatic clearance compensation device for a support yoke of a rack-pinion type steering apparatus which can automatically compensate for a clearance generated at the support yoke due to a long-term use of the rack-pinion type steering apparatus without a separate adjusting work.
2. Description of the Prior Art
In general, a steering apparatus refers to a device to change the travelling direction of a vehicle according to a driver's intent. The steering device is an auxiliary device to change a rotational center about which a front wheel is pivoted so as to move the vehicle in a direction where the driver wants to go.
FIG. 1 is a schematic view illustrating a conventional rack-pinion type steering apparatus of a vehicle, and FIG. 2 is a side elevation cross-sectional view illustrating a gearbox provided in the conventional rack-pinion type steering apparatus.
Referring to FIG. 1, a rack-pinion type steering apparatus of the vehicle includes a steering wheel 100 disposed at a driver's seat, a steering shaft 105 connected to the steering wheel 100, a steering column 103 to secure the steering shaft 105 to a vehicle body (not shown), a gearbox 130 having a rack gear 110 and a pinion gear 120 to convert a rotational force inputted from the steering shaft 105 into a linear movement, a rack bar 140 provided with inner ball joints 145 at its opposite ends, a tie rod 150 integrally formed with a ball of the inner ball joint 145, and outer ball joints 155 provided at the end of the tie rod 150. The tie rod 150 is connected with a knuckle 165 of a tire 160 through the outer ball joints 155. A reference numeral 170 denotes a rack housing to accommodate the rack bar 140.
As shown in FIG. 2, the gearbox 130 provided in the conventional rack-pinion type steering apparatus includes a pinion shaft 220, a rack bar 140, a support yoke 230, a spring 235, a yoke plug 240, and a rack housing 170. This gearbox 130, as described above, converts a rotational force inputted from the steering shaft 105 (see FIG. 1) into a linear movement.
The pinion shaft 220 receives a rotational force from an input shaft 210 connected with the steering shaft 105 and delivers the same to the rack bar 140. Here, the pinion shaft 220 is connected to the input shaft 210 through a torsion bar 215. Formed on the distal end of the pinion shaft 220 is a pinion gear 120 to be engaged with a rack gear 110 (see FIG. 1) of the rack bar 140.
The rack bar 140, cooperating with the pinion shaft 220, is designed to convert a rotational movement into a linear movement. The rack bar 140 is shaped like a bar to traverse to the front wheels of the vehicle. The rack bar 140 is formed with a rack gear 110 on one side of the opposite inner ball joints 145, wherein the rack gear 110 is engaged with the pinion gear 120 of the pinion shaft 220.
Meanwhile, the support yoke 230 is designed to reduce a clearance between the rack bar 140 and the pinion shaft 220, so as to smoothly deliver the power. The support yoke 230 is positioned at the rear side of the rack bar 140, i.e., an opposite side of the surface on which the rack gear 110 is formed. The support yoke 230 has a structure displaceable back and forth, while inserted in the rack housing 170 formed in a cylinder shape.
The support yoke 230 is shaped like a cylinder capable of slidably moving back and forth within the cylinder of the rack housing 170, and the front portion of the rack bar 140 is formed in a semi-circular groove to be closely in contact with the rear surface of the rack bar 140.
The front portion of the support yoke 230 as such experiences a sliding friction with the rear surface of the rack bar 140. In order to prevent wear and noise of the rack bar 140 due to such a friction, the support yoke 230 is generally made from a plastic or other much softer material than that of the rack bar 140.
To enable the rack bar 140 to be closely brought into contact with the pinion shaft 220 and deliver the power efficiently, a spring 235 is disposed at the rear side of the support yoke 230. The spring 235 pushes the support yoke 230 with a constant pressure, so that the support yoke 230 can closely make contact with the rack bar 140 to compensate for the clearance created between the rack bar 140 and the pinion shaft 220. A coil spring is commonly used for the spring 235, which is supported by a yoke plug 240.
The yoke plug 240 supports the spring 235 to apply a resilient force to the support yoke 230. The yoke plug 240 is generally formed with a male screw portion which can be engaged with the rack housing 170 formed with a female screw portion. The yoke plug 240 is provided with a recess (not shown) on its rear surface in which a wrench can be inserted. Hence, when the yoke plug 240 is coupled to the rack housing 170 or when a severe clearance is created between the rack bar 140 and the pinion shaft 220, the tensional force of the spring 235 is adjustable by tightening the yoke plug 240 with a wrench.
However, it should be noted that due to a long-term use of the steering apparatus, the support yoke 230 gradually moves towards the rack bar 140, which increases the clearance between the yoke plug 240 and the support yoke 230, thereby producing a large noise because of vibrations therebetween.
Besides, it should be appreciated that even though there is no increase in the clearance, the rack bar 140 moves instantly due to external impacts reversely transmitted from the tire 160 (see FIG. 1) when the vehicle travels on irregular road surfaces, such that the support yoke 230 is collided with the yoke plug 240 to cause noise.